In the title compound, C29H23N3O4, the 2-methylpyrrolidine ring adopts a twist conformation on the N—C bond involving the spiro C atom, while the hydropyran ring adopts an envelope conformation with the methine C atom bonded to the O atom as the flap. The mean plane of the indoline-2-one ring system is almost perpendicular to the mean plane of the pyrrolidine ring, making a dihedral angle of 89.73 (8)°. The latter ring makes dihedral angles of 47.80 (8) with the naphthalene ring system and 32.38 (8)° with the hydropyran ring mean plane. There is an intra­molecular C-H⋯O hydrogen bond involving the indoline-2-one O atom. In the crystal, adjacent mol­ecules are linked via N—H⋯O hydrogen bonds, forming chains propagating along [100]. The chains are linked via weak C—H⋯O hydrogen bonds, forming two-dimensional networks, lying parallel to (101), and consolidated by C—H⋯π inter­actions.

4H-chromenes are biologically important compounds used as synthetic ligands in the design of drugs and discovery processes. They exhibit numerous biological and pharmacological properties, such as anti-viral, anti-fungal, antiinflammatory, anti- diabetic, cardionthonic, anti anaphylactic and anti-cancer (Cai, 2008, 2007; Cai et al., 2006; Gabor, 1988; Brooks, 1998; Valenti et al., 1993; Hyana & Saimoto, 1987; Tang et al., 2007). Indoline-2-one and its derivatives have been used as precursors to synthesis pharmaceuticals (Colgan et al., 1996). Continuing our interest in such compounds we have synthesized the title compound and report herein on its crystal structure.

In the title compound, Fig. 1, the pyrrole ring (N2/C7/C8/C20/C21) adopts a twist conformation on bond C21-N2, while the pyran ring (O1/C1/C6-C9) adopts a envelope conformation with atom C9 as the flap. The pyrrole ring (N2/C7/C8/C20/C21) mean plane makes a dihedral angle of 89.73 (8)° with the mean plane of the indoline-2-one ring system (N3/C21-C28), which shows that they are almost orthogonal to each other. The same pyrrole ring mean plane makes dihedral angles of 47.80 (8) Å with the naphthalene ring system (C10-C19) and 32.38 (8)° with the pyran ring mean plane (O1/C1/C6-C9), and the oxygen atom O4 attached to the pyrrole ring deviates by -0.0886 (2) Å. The nitro group (N1/O2/O3) is inclined to the mean plane of the pyrrole ring, to which it is attached, with a dihedral angle of 50.76 (19) °.

To a solution of isatin (1 equiv) and sarcosine (1.4 equiv) in dry toluene, was added 2-(naphthalen-1-yl)-3-nitro-2H-chromene (1 equiv) under a nitrogen atmosphere. The reaction mixture was refluxed for 24h in a Dean-Stark apparatus to give the cycloadducts. After completion of the reaction as indicated by TLC, the solvent was evaporated under reduced pressure. The crude product was extracted with dichloromethane. The organic layer was dried with anhydrous sodium sulphate and concentrated in vacuo. The crude product obtained was purified by column chromatography using hexane/EtOAc (7:3) as eluent. Single crystals suitable for X-ray diffraction were obtained by slow evaporation of a solution of the title compound in ethyl acetate at room temperature.

The NH H atom was located in a difference Fourier map and refined with a distance restraint of N-H = 0.88 (1) Å with Uiso(H) = 1.2Ueq(N). The C-bound H atoms were placed in calculated positions and treated as riding atoms: C—H = 0.93 - 0.97 Å, with Uiso(H) = 1.5Ueq(C) for methyl H atoms and = 1.2Ueq(C) for other H atoms.

Fig. 1. The molecular structure of the title molecule, with atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

Fig. 2. A partial view, ca. perpendicular to (110), of the crystal packing of the title compound. The hydrogen bonds are shown as dashed lines - see Table 1 for details; H-atoms not involved in hydrogen bonding have been omitted for clarity.

2-Methyl-4-(naphthalen-2-yl)-3a-nitro-3,3a,4,9b-tetrahydro-2H-spiro[chromeno[3,4-c]pyrrole-1,3'-indolin]-2'-one top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2sigma(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Acknowledgements

The authors thank the TBI X-ray facility, CAS in Crystallography and Biophysics, University of Madras, India, for the data collection. SK, TS and DV thank the UGC (SAP–CAS) for the departmental facilities. SK also thanks DST PURSE for a Junior Research Fellowship and TS also thanks DST Inspire for a fellowship.

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